The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Dual clutch transmissions are a relatively recent addition to the stable of motor vehicle transmissions which previously included manual, continuously variable and automatic transmissions. Dual clutch transmissions or DCT's as they are now commonly known, combine good fuel economy with rapidly executed shifts. From a performance standpoint, therefore, they closely duplicate the feel and operation of a conventional mechanical transmission. Additionally, they may be configured to operate as an essentially automatic or manual transmission and thus exhibit exceptional versatility.
Structurally, dual clutch transmissions typically include an input shaft which drives a pair of mutually exclusively engaged input clutches. The input clutches drive a pair of countershafts which each include a plurality of gears freely rotatably disposed on the countershafts and associated synchronizer clutches. The pluralities of gears are in constant mesh with gears secured to an output shaft. Activation of a synchronizer clutch synchronizes and couples a selected gear to its countershaft. Then, the input clutch associated with that countershaft is engaged to transmit torque from the input shaft to the output shaft. Because clutches, gears and synchronizers are disposed or stacked along the countershafts, the axial length of dual clutch transmissions can create packaging issues, particularly in smaller vehicles.
While there are various ways to classify or categorize dual clutch transmissions, one approach to classification relates to the type of clutch utilized in the transmission: wet or dry. A wet dual clutch transmission contains lubricating transmission fluid not only in the gear and synchronizer section but also in the input clutches. A dry dual clutch transmission, of course, includes transmission fluid in the gear and synchronizer section but not in the clutches. While wet dual clutch transmissions offer slightly better durability and longer clutch life because of the cooling provided by the transmission fluid, they exhibit higher spin losses. Moreover, the incorporation of a lubrication pump which provides pressurized lubricating and cooling fluid further affects overall efficiency. Accordingly, wet dual clutch transmissions, all other parameters being equal, typically exhibit slightly lower fuel economy than dry dual clutch transmissions.
From the foregoing, it is apparent that improvements addressing both packaging and efficiency issues of dual clutch transmissions are both desirable and possible. The present invention is so directed.